1. Field of the Invention
The present invention relates to a film changer for an X-ray examination diagnostics installation, and a method for operating the film changer, and in particular to such a film changer and method for operating same which permits optional examination of a patient by radiographic or fluoroscopic means.
2. Description of the Prior Art
Frequently during X-ray examination of a patient, the desire to switch from one mode of examination, such as radiographic examination, to another mode of examination, such as fluoroscopic examination, is desired. As used herein, radiographic examination means the generation of a static shadowgraph, while the term fluoroscopy as used herein refers to generation of a dynamic X-ray image. During fluoroscopic examination, no components which may attenuate the incident radiation can be present in front of the X-ray image intensifier. As described in European patent application No. ER 0,003 691 B 1, an X-ray examination apparatus has an X-ray image intensifier and an X-ray film changer disposed at fixed positions relative to each other, and the recording unit has a recording window for use with the X-ray image intensifier and a pressure plate for maintaining screen foils used in radiographic examinations in place. The screen foil is manually withdrawn from the film changer when fluoroscopic examination is desired. This permits the x-radiation to proceed unimpeded to the X-ray image intensifier through the X-ray film changer.
In angiographic examinations, a contrast agent is injected into the blood vessels of a patient and is tracked using the X-ray image intensifier. If the physician or technician wishes to quickly make an X-ray shadowgraph or radiograph during such an examination, the exposure and its associated components must again be inserted. This may take such a long time, given conventional devices, that the desired radiograph cannot be made in time. Such an X-ray apparatus is therefore not suitable for examinations wherein a rapid change between radiographic and fluoroscopic examinations may be moving.
A film changer is disclosed in U.S. Pat. No. 4,199,687 which permits switching between a radiographic examination mode and a fluoroscopic examination mode. For this purpose, screen foils used in the radiographic examination are secured to a long conveyor belt by means of which the foils are transported into the recording unit or out of the recording unit, as needed. Each conveyor belt is actuated by a transport device having deflection rolls, auxiliary rolls, and take-up rolls. In order to permit the film conveying track to be free between the supply and takeup magazines, the conveyor with the rolls for upper screen foil is attached above the film conveying track, and the conveyor belt with the rolls for the lower screen foil is attached below the film conveying track. This device is mechanically complex and space-consuming, with the result that the film changer as a unit is relatively bulky. Moreover, the screen foils, in particular the lower screen foil, are difficult to access. A further disadvantage is that the screen foils must be loosened from the conveyor belt when being cleaned and replaced.